Binders are useful in fabricating materials from non-assembled or loosely-assembled matter. For example, binders enable two or more surfaces to become united. Binders may be broadly classified into two main groups: organic and inorganic, with the organic materials being subdivided into those of animal, vegetable, and synthetic origin. Another way of classifying binders is based upon the chemical nature of these compounds: (1) protein or protein derivatives; (2) starch, cellulose, or gums and their derivatives; (3) thermoplastic synthetic resins; (4) thermosetting synthetic resins; (5) natural resins and bitumens; (6) natural and synthetic rubbers; and (7) inorganic binders. Binders also may be classified according to the purpose for which they are used: (1) bonding rigid surfaces, such as rigid plastics, and metals; and (2) bonding flexible surfaces, such as flexible plastics, and thin metallic sheets.
Thermosetting synthetic resins comprise a variety of phenol-aldehyde, urea-aldehyde, melamine-aldehyde, and other condensation-polymerization materials, such as the furane and polyurethane resins. Thermosetting synthetic resins may be characterized by being transformed into insoluble and infusible materials, i.e., thermoset binders, by means of either heat or catalytic action. Thermoset binder compositions containing phenol-formaldehyde, urea-formaldehyde, melamine-formaldehyde, and like combinations are used for the bonding of glass fibers, textiles, plastics, rubbers, and many other materials.
Resole resin is a phenol-aldehyde thermosetting synthetic resin having a molar ratio of phenol to aldehyde in the range from about 1:1.1 to about 1:5. Preferably, the molar ratio of phenol to aldehyde ranges from about 1:2 to about 1:3. The phenol component of the resole resin can include a variety of substituted and unsubstituted phenolic compounds. The aldehyde component of the resole resin is preferably formaldehyde, but can include so-called masked aldehydes or aldehyde equivalents such as acetals or hemiacetals. Specific examples of suitable aldehydes include: formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, furfuraldehyde, and benzaldehyde.
Phenol-formaldehyde (PF) resole resins, as well as phenol-formaldehyde resole resins extended with urea (PFU resins), are used in conventional processes, and have been relied on heavily over the past several years to prepare PF and PFU thermoset binders, respectively, for fiberglass insulation products. Though PFU binders are more cost-effective than PF binders and provide cured fiberglass insulation products with the requisite physical properties (e.g., flexural rigidity, tensile strength, bond strength, parting strength) and the desired thermal and acoustical performance, PFU binders may exhibit some loss in thermoset properties as the urea content increases. Further, in addition to occasionally having a distinctive or unpleasant odor, owing to the presence of formaldehyde and/or trimethylamine (the latter a byproduct of scavenging formaldehyde with urea), the resulting cured products may have a formaldehyde and/or trimethylamine content that may limit the use of PFU binders in certain applications.
Accordingly, efforts have been made to incorporate other resins and/or additives into PFU binders that can enhance, or at least not diminish, the desired properties of the resulting thermoset binder, while yielding a lower formaldehyde-emission and/or lower trimethylamine-emission product. Further, as indicated above, binders are useful in fabricating materials from non-assembled or loosely-assembled matter. Thus, notwithstanding a binder's formaldehyde and/or trimethylamine content, which content may immediately or eventually restrict its use, compositions capable of functioning as a binder are desirable.